What constitutes a Service Provider in the world of PCI?

The PCI SSC defines a Service Provider this way:“Business entity that is not a payment brand, directly involved in the processing, storage, or transmission of cardholder data. This also includes companies that provide services that control or could impact the security of cardholder data.” (Source: www.pcisecuritystandards.org)

The “merchant as a service provider” role is further specified by the PCI SSC as “a merchant that accepts payment cards as payment for goods and/or services…if the services sold result in storing, processing, or transmitting cardholder data on behalf of other merchants or service providers.”